In recent years, organic EL (Electro Luminescence) display devices have been drawing public attention as a display of the next generation. With organic EL display devices that are currently mass-produced, the formation of an organic EL layer is primarily done by using a vacuum vapor deposition method.
Typically, a mask made of a metal (a metal mask) is used as the vapor deposition mask. However, with the increasing definition of organic EL display devices, it is becoming difficult to precisely form a vapor deposition pattern using a metal mask. This is because it is difficult with current metal processing techniques to precisely form small openings corresponding to a short pixel pitch (e.g., about 10 to 20 μm) in a metal plate (e.g., a thickness of about 100 μm) to be the metal mask.
In view of this, a vapor deposition mask (hereinafter referred to also as a “layered mask”) having a structure in which a resin layer and a metal layer are layered together has been proposed in the art as a vapor deposition mask for forming a vapor deposition pattern with a high definition.
For example, Patent Document No. 1 discloses a layered mask including a resin film layered with a hold member, which is a metal magnetic member. A plurality of openings corresponding to an intended vapor deposition pattern are formed in the resin film. Slits whose size is larger than the openings of the resin film are formed in the hold member. The openings of the resin film are arranged in the slits. Therefore, when the layered mask of Patent Document No. 1 is used, the vapor deposition pattern is formed corresponding to the plurality of openings of the resin film. Even small openings can be formed with a high precision in a resin film that is thinner than an ordinary metal plate used for a metal mask.
When forming small openings as described above in the resin film, a laser ablation method is suitably used. Patent Document No. 1 describes a method in which a resin film placed on a support member (e.g., a glass substrate) is irradiated with a laser so as to form openings of an intended size.
FIGS. 28(a) to 28(d) are schematic cross-sectional views each illustrating a step of a conventional method for manufacturing a vapor deposition mask disclosed in Patent Document No. 1.
According to Patent Document No. 1, first, as shown in FIG. 28(a), a metal layer 82 having openings (slits) 85 therein is formed on a resin film 81, thereby obtaining a layered film 80. Then, as shown in FIG. 28(b), the layered film 80 is attached to a frame 87 with tension in a predetermined in-plane direction(s) applied on the layered film 80. Then, the layered film 80 is placed on a glass substrate 90 as shown in FIG. 28(c). In this process, a surface of the resin film 81 that is opposite from the metal layer 82 is brought into close contact with the glass substrate 90 with a liquid 88 such as ethanol therebetween. Then, as shown in FIG. 28(d), portions of the resin film 81 that is exposed through the slits 85 of the metal layer 82 are irradiated with a laser beam L, thereby forming a plurality of openings 89 in the resin film 81. Thus, a layered vapor deposition mask 900 is manufactured.